It is estimated that there are 100,000 amputations annually in the United States for ischemic disease of the lower extremity. Inadequate blood flow to the skin of the leg is not only the primary cause for these amputations, but also for non-healing of the site following amputation. No clinical method currently exists to evaluate the level and adequacy of the cutaneous flow in the ischemic limbs. In this study we propose to evaluate the skin blood flow in the affected extremity using the 133xenon radiotracer clearance technique in combinatton with a stress test which measures the response of the skin blood flow to a graded, externally applied pressure load. Pressures applied will range from 0 to 150 mm Hg, and simultaneous flows will be measured with a continuously recording, non-invasive laser Doppler velocimetry system. The hypothesis to be tested is that skin blood flow in ischemic limbs will decrease more in response to a pressure load than it will in normals, and that this represents a more critical test of cutaneous flow reserve than does resting skin blood flow.